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authorIvan Tubert-Brohman <itub@cpan.org>2005-10-12 15:20:18 -0400
committerRafael Garcia-Suarez <rgarciasuarez@gmail.com>2005-10-13 11:20:23 +0000
commitd74e8afc9309529cf5c6c4390fc311850865d506 (patch)
treee2e6f5cb76495c762f9de01020f6d7eae39011dd /pod/perlfaq5.pod
parentfab416db1cda0a357b1699b6efa75dd50332ea26 (diff)
downloadperl-d74e8afc9309529cf5c6c4390fc311850865d506.tar.gz
POD index entries with X<>
Message-ID: <434D9A32.4050305@cpan.org> p4raw-id: //depot/perl@25748
Diffstat (limited to 'pod/perlfaq5.pod')
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diff --git a/pod/perlfaq5.pod b/pod/perlfaq5.pod
index 85f1c546e5..bab49a2130 100644
--- a/pod/perlfaq5.pod
+++ b/pod/perlfaq5.pod
@@ -8,6 +8,7 @@ This section deals with I/O and the "f" issues: filehandles, flushing,
formats, and footers.
=head2 How do I flush/unbuffer an output filehandle? Why must I do this?
+X<flush> X<buffer> X<unbuffer> X<autoflush>
Perl does not support truly unbuffered output (except
insofar as you can C<syswrite(OUT, $char, 1)>), although it
@@ -61,11 +62,13 @@ or IO::Socket:
$sock->autoflush();
=head2 How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file?
+X<file, editing>
Use the Tie::File module, which is included in the standard
distribution since Perl 5.8.0.
=head2 How do I count the number of lines in a file?
+X<file, counting lines> X<lines> X<line>
One fairly efficient way is to count newlines in the file. The
following program uses a feature of tr///, as documented in L<perlop>.
@@ -82,6 +85,7 @@ proper text file, so this may report one fewer line than you expect.
This assumes no funny games with newline translations.
=head2 How can I use Perl's C<-i> option from within a program?
+X<-i> X<in-place>
C<-i> sets the value of Perl's C<$^I> variable, which in turn affects
the behavior of C<< <> >>; see L<perlrun> for more details. By
@@ -107,6 +111,7 @@ leaving a backup of the original data from each file in a new
C<.c.orig> file.
=head2 How can I copy a file?
+X<copy> X<file, copy>
(contributed by brian d foy)
@@ -123,6 +128,7 @@ open the original file, open the destination file, then print
to the destination file as you read the original.
=head2 How do I make a temporary file name?
+X<file, temporary>
If you don't need to know the name of the file, you can use C<open()>
with C<undef> in place of the file name. The C<open()> function
@@ -175,6 +181,7 @@ temporary files in one process, use a counter:
}
=head2 How can I manipulate fixed-record-length files?
+X<fixed-length> X<file, fixed-length records>
The most efficient way is using L<pack()|perlfunc/"pack"> and
L<unpack()|perlfunc/"unpack">. This is faster than using
@@ -206,6 +213,7 @@ group or loop over them with for. It also avoids polluting the program
with global variables and using symbolic references.
=head2 How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles?
+X<filehandle, local> X<filehandle, passing> X<filehandle, reference>
As of perl5.6, open() autovivifies file and directory handles
as references if you pass it an uninitialized scalar variable.
@@ -234,6 +242,7 @@ If you want to create many anonymous handles, you should
check out the Symbol or IO::Handle modules.
=head2 How can I use a filehandle indirectly?
+X<filehandle, indirect>
An indirect filehandle is using something other than a symbol
in a place that a filehandle is expected. Here are ways
@@ -329,15 +338,18 @@ It's the syntax of the fundamental operators. Playing the object
game doesn't help you at all here.
=head2 How can I set up a footer format to be used with write()?
+X<footer>
There's no builtin way to do this, but L<perlform> has a couple of
techniques to make it possible for the intrepid hacker.
=head2 How can I write() into a string?
+X<write, into a string>
See L<perlform/"Accessing Formatting Internals"> for an swrite() function.
=head2 How can I output my numbers with commas added?
+X<number, commify>
(contributed by brian d foy and Benjamin Goldberg)
@@ -373,6 +385,7 @@ It is easier to see with comments:
)/$1,/xg;
=head2 How can I translate tildes (~) in a filename?
+X<tilde> X<tilde expansion>
Use the <> (glob()) operator, documented in L<perlfunc>. Older
versions of Perl require that you have a shell installed that groks
@@ -395,6 +408,7 @@ Within Perl, you may use this directly:
}ex;
=head2 How come when I open a file read-write it wipes it out?
+X<clobber> X<read-write> X<clobbering> X<truncate> X<truncating>
Because you're using something like this, which truncates the file and
I<then> gives you read-write access:
@@ -468,6 +482,7 @@ isn't as exclusive as you might wish.
See also the new L<perlopentut> if you have it (new for 5.6).
=head2 Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>?
+X<argument list too long>
The C<< <> >> operator performs a globbing operation (see above).
In Perl versions earlier than v5.6.0, the internal glob() operator forks
@@ -481,6 +496,7 @@ yourself with readdir() and patterns, or use a module like File::KGlob,
one that doesn't use the shell to do globbing.
=head2 Is there a leak/bug in glob()?
+X<glob>
Due to the current implementation on some operating systems, when you
use the glob() function or its angle-bracket alias in a scalar
@@ -488,6 +504,7 @@ context, you may cause a memory leak and/or unpredictable behavior. It's
best therefore to use glob() only in list context.
=head2 How can I open a file with a leading ">" or trailing blanks?
+X<filename, special characters>
(contributed by Brian McCauley)
@@ -504,6 +521,7 @@ charcters in the filename as special.
open FILE, ">", ">file"; # filename is ">file"
=head2 How can I reliably rename a file?
+X<rename> X<mv> X<move> X<file, rename> X<ren>
If your operating system supports a proper mv(1) utility or its
functional equivalent, this works:
@@ -519,6 +537,7 @@ permissions, timestamps, inode info, etc.
Newer versions of File::Copy export a move() function.
=head2 How can I lock a file?
+X<lock> X<file, lock> X<flock>
Perl's builtin flock() function (see L<perlfunc> for details) will call
flock(2) if that exists, fcntl(2) if it doesn't (on perl version 5.004 and
@@ -566,6 +585,7 @@ L<perlopentut/"File Locking"> if you have it (new for 5.6).
=back
=head2 Why can't I just open(FH, "E<gt>file.lock")?
+X<lock, lockfile race condition>
A common bit of code B<NOT TO USE> is this:
@@ -585,6 +605,7 @@ Various schemes involving link() have been suggested, but
these tend to involve busy-wait, which is also subdesirable.
=head2 I still don't get locking. I just want to increment the number in the file. How can I do this?
+X<counter> X<file, counter>
Didn't anyone ever tell you web-page hit counters were useless?
They don't count number of hits, they're a waste of time, and they serve
@@ -609,6 +630,7 @@ Here's a much better web-page hit counter:
If the count doesn't impress your friends, then the code might. :-)
=head2 All I want to do is append a small amount of text to the end of a file. Do I still have to use locking?
+X<append> X<file, append>
If you are on a system that correctly implements flock() and you use the
example appending code from "perldoc -f flock" everything will be OK
@@ -637,6 +659,7 @@ level write()s even if the buffer was empty to start. There may be some
systems where this probability is reduced to zero.
=head2 How do I randomly update a binary file?
+X<file, binary patch>
If you're just trying to patch a binary, in many cases something as
simple as this works:
@@ -660,6 +683,7 @@ Locking and error checking are left as an exercise for the reader.
Don't forget them or you'll be quite sorry.
=head2 How do I get a file's timestamp in perl?
+X<timestamp> X<file, timestamp>
If you want to retrieve the time at which the file was last
read, written, or had its meta-data (owner, etc) changed,
@@ -693,6 +717,7 @@ in theory, independent of the current locale. See L<perllocale>
for details.
=head2 How do I set a file's timestamp in perl?
+X<timestamp> X<file, timestamp>
You use the utime() function documented in L<perlfunc/utime>.
By way of example, here's a little program that copies the
@@ -718,6 +743,7 @@ a finer granularity than two seconds. This is a limitation of
the filesystems, not of utime().
=head2 How do I print to more than one file at once?
+X<print, to multiple files>
To connect one filehandle to several output filehandles,
you can use the IO::Tee or Tie::FileHandle::Multiplex modules.
@@ -728,6 +754,7 @@ to each filehandle.
for $fh (FH1, FH2, FH3) { print $fh "whatever\n" }
=head2 How can I read in an entire file all at once?
+X<slurp> X<file, slurping>
You can use the File::Slurp module to do it in one step.
@@ -781,6 +808,7 @@ The third argument tests the byte size of the data on the INPUT filehandle
and reads that many bytes into the buffer $var.
=head2 How can I read in a file by paragraphs?
+X<file, reading by paragraphs>
Use the C<$/> variable (see L<perlvar> for details). You can either
set it to C<""> to eliminate empty paragraphs (C<"abc\n\n\n\ndef">,
@@ -791,6 +819,7 @@ Note that a blank line must have no blanks in it. Thus
S<C<"fred\n \nstuff\n\n">> is one paragraph, but C<"fred\n\nstuff\n\n"> is two.
=head2 How can I read a single character from a file? From the keyboard?
+X<getc> X<file, reading one character at a time>
You can use the builtin C<getc()> function for most filehandles, but
it won't (easily) work on a terminal device. For STDIN, either use
@@ -922,6 +951,7 @@ FIONREAD requires a filehandle connected to a stream, meaning that sockets,
pipes, and tty devices work, but I<not> files.
=head2 How do I do a C<tail -f> in perl?
+X<tail>
First try
@@ -950,6 +980,7 @@ more. Lather, rinse, repeat.
There's also a File::Tail module from CPAN.
=head2 How do I dup() a filehandle in Perl?
+X<dup>
If you check L<perlfunc/open>, you'll see that several of the ways
to call open() should do the trick. For example:
@@ -970,6 +1001,7 @@ a copied one.
Error checking, as always, has been left as an exercise for the reader.
=head2 How do I close a file descriptor by number?
+X<file, closing file descriptors>
This should rarely be necessary, as the Perl close() function is to be
used for things that Perl opened itself, even if it was a dup of a
@@ -989,6 +1021,7 @@ Or, just use the fdopen(3S) feature of open():
}
=head2 Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe` work?
+X<filename, DOS issues>
Whoops! You just put a tab and a formfeed into that filename!
Remember that within double quoted strings ("like\this"), the
@@ -1005,6 +1038,7 @@ awk, Tcl, Java, or Python, just to mention a few. POSIX paths
are more portable, too.
=head2 Why doesn't glob("*.*") get all the files?
+X<glob>
Because even on non-Unix ports, Perl's glob function follows standard
Unix globbing semantics. You'll need C<glob("*")> to get all (non-hidden)
@@ -1027,6 +1061,7 @@ of the directory, not of the file). If you try to write to the file,
the permissions of the file govern whether you're allowed to.
=head2 How do I select a random line from a file?
+X<file, selecting a random line>
Here's an algorithm from the Camel Book: